Disentangling the roles of mobility and propagule pressure in species responses to landscape structure

物种灭绝主要是由于自然栖息地的丧失，特别是在加拿大南部等原生生物多样性高的地区。有人建议将连通性保护作为减缓这些地区物种损失的一种手段。在具有高连通性的景观中，自然栖息地的安排使得生物可以安全地在残余栖息地斑块之间移动。连通性保护保留了连接栖息地斑块的自然栖息地要素（例如灌木树篱）。 这种对连通性保护的强调主要源于研究表明，具有较高传播能力的物种更有可能在人类改造的景观中持续存在。然而，连通性守恒和扩散能力之间的联系并不简单，因为扩散能力是以两种方式概念化的：（i）移动性-个体移动到遥远地点的能力-和（ii）殖民能力-物种殖民遥远地点的能力。定殖能力取决于移动性和分散个体的数量，称为繁殖体压力。种群压力又取决于种群规模和繁殖力。超过90%的研究表明，物种对景观结构（森林数量、道路密度等）的响应中，扩散能力的作用。以结合联合收割机移动性和繁殖压力的方式来测量扩散能力。这是有问题的，因为，如果传播能力更强烈地由繁殖压力比流动性驱动，那么，而不是优先考虑连接保护，我们应该集中精力增加繁殖压力，通过增加栖息地的数量和质量。这将增加种群规模和繁殖力，从而增加分散个体的数量（繁殖体压力）。 我建议确定的作用，流动性本身的物种对景观结构的反应。我们将进行空间模拟，以预测流动性或繁殖体压力应驱动物种反应的情况。我们将进行元分析，以确定知识的现状，我们将进行模型预测的实证检验，使用我们自己和其他人的现有数据，在广泛的分类群，并收集额外的数据在需要的地方。总体而言，我预测，流动性在物种对景观结构的反应中起着次要作用，尽管我准备对结果感到惊讶。但如果我是正确的，那么保护工作的目标应该是最大限度地提高栖息地的总面积和质量，而不管它在促进迁徙方面的假定作用。换句话说，政府和非政府组织应该抓住并鼓励每一个机会来保护，恢复和改善自然栖息地，因为即使是小的或孤立的地块也会增加种群规模，从而增加繁殖压力。

Species extinctions are driven mainly by loss of natural habitats, especially in regions with high native biodiversity such as southern Canada. Connectivity conservation has been suggested as a means of slowing species losses in such regions. In a landscape with high connectivity the natural habitat is arranged such that organisms can safely move between remnant habitat patches. Connectivity conservation preserves elements of natural habitat (e.g. hedgerows) that link habitat patches. This emphasis on connectivity conservation arises largely from research suggesting that species with higher dispersal abilities are more likely to persist in human-modified landscapes. However, the link between connectivity conservation and dispersal ability is not straightforward, because dispersal ability is conceptualized in two ways: (i) mobility - the ability of individuals to move to distant sites -, and (ii) colonizing ability - the ability of a species to colonize distant sites. Colonizing ability depends on both mobility and the number of dispersing individuals, called propagule pressure. Propagule pressure, in turn, depends on population size and fecundity. Over 90% of studies of the role of dispersal ability in species responses to landscape structure (forest amount, road density etc.) measure dispersal ability in ways that combine mobility and propagule pressure. This is problematic because, if dispersal ability is more strongly driven by propagule pressure than by mobility then, rather than prioritizing connectivity conservation, we should focus efforts on increasing propagule pressure by increasing habitat amount and quality. This will increase population sizes and fecundity and therefore increase the number of dispersing individuals (propagule pressure). I propose to determine the role of mobility itself in species responses to landscape structure. We will conduct spatial simulations to predict situations when mobility or propagule pressure should drive species responses. We will conduct meta-analyses to determine the current state of knowledge, and we will conduct empirical tests of the model predictions, using our own and others' existing data on a wide range of taxa, and collecting additional data where needed. Overall, I predict that mobility plays a minor role in species responses to landscape structure, though I am prepared to be surprised by the results. But if I am correct, then conservation efforts should aim to maximize the total area and quality of habitat, irrespective of its presumed role in facilitating movement. In other words, governments and NGO's should take and encourage every opportunity to preserve, restore, and improve natural habitat, because even small or isolated parcels can increase population size and therefore increase propagule pressure.